Heavy cream makes a huge difference in texture and taste. When I went to Hershey, PA a few years ago, we were trying to figure out why the chocolate milk was so extra-amazing there. Pretty sure it was mostly heavy cream with a splash of milk. Crazy calorific, but delicious.
I had a stockpile of chocolate Metabolic Drive and different MAG-10 liquid flavoring a while ago, so I tried some of the flavorings in the Metabolic Drive. Orange flavoring with chocolate protein is a wild combo that works. Sweet, but not too strong because the chocolate dials it down. Berry and chocolate is alright, almost like chocolate-covered strawberry or something. Grape and chocolate, well, didn't work so well.
Not quite shakes, but I'm getting better at making "protein pudding" quick from scratch. One scoop Metabolic Drive, a little less than one Tablespoon peanut butter, and I'm still working on eyeballing the water to get the right consistency. Sometimes I'll fork-smash a banana in the bowl first, then add the same other ingredients.